Aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid or their di-esters, dimethyl terephthalate as for example, are used to produce a variety of polyester products, important examples of which are poly(ethylene terephthalate) and its copolymers. The aromatic dicarboxylic acids are synthesized by the catalytic oxidation of the corresponding dialkyl aromatic compounds which are obtained from fossil fuels (US 2006/0205977 A1). Esterification of these diacids using excess alcohol produces the corresponding di-esters (US2010/0210867A1). There is a growing interest in the use of renewable resources as feed stocks for the chemical industries mainly due to the progressive reduction of fossil reserves and their related environmental impacts.
Furan-2,5-dicarboxylic acid (FDCA) is a versatile intermediate considered as a promising closest biobased alternative to terephthalic acid and isophthalic acid. Like aromatic diacids, FDCA can be condensed with diols such as ethylene glycol to make polyester resins similar to polyethylene terephthalate (PET) (Gandini, A.; Silvestre, A. J; Neto, C. P.; Sousa, A. F.; Gomes, M., J. Poly. Sci. A 2009, 47, 295). FDCA has been prepared by oxidation of 5-(hydroxymethyl) furfural (5-HMF) under air using homogenous catalysts (US2003/0055271 A1 and Partenheimer, W.; Grushin, V. V., Adv. Synth. Catal. 2001, 343, 102-111.) but only a maximum of 44.8% yield using a Co/Mn/Br catalyst system and a maximum of 60.9% yield was reported using Co/Mn/Br/Zr catalysts combination. Recently, we reported a process for producing furan-2,5-dicarboxylic acid (FDCA) in high yields by liquid phase oxidation of 5-HMF or its derivatives using a Co/Mn/Br catalyst system that minimizes solvent and starting material loss through carbon burn (U.S. patent application Ser. Nos. 13/228,803, 13/228,809, 13/228,816, and 13/228,799, herein incorporated by reference).
Disclosed is a method for recovering a portion of oxidation solvent, a portion of oxidation catalyst, and removing a portion of oxidation by-products and raw material impurities from a solvent stream generated in a process to make furan-2,5-dicarboxylic acid (FDCA). The process comprises oxidizing a feed stream comprising at least one oxidizable compound selected from the following group: 5-(hydroxymethyl)furfural (5-HMF), 5-HMF esters (5-R(CO)OCH2-furfural where R=alkyl, cycloalkyl and aryl), 5-HMF ethers (5-R′OCH2-furfural, where R′=alkyl, cycloalkyl and aryl), 5-alkyl furfurals (5-R″-furfural, where R″=alkyl, cycloalkyl and aryl), mixed feed-stocks of 5-HMF and 5-HMF esters and mixed feed-stocks of 5-HMF and 5-HMF ethers and mixed feed-stocks of 5-HMF and 5-alkyl furfurals to generate a crude carboxylic acid slurry comprising furan-2,5-dicarboxylic acid (FDCA) in an oxidation zone, cooling a crude carboxylic acid slurry in a cooling zone to generate a cooled crude carboxylic acid slurry, removing impurities from a cooled crude carboxylic acid slurry in a solid-liquid separation zone to form a low impurity carboxylic acid stream and a mother liquor stream, routing at least a portion of the mother liquor stream to a mother liquor purge zone to generate a recycle oxidation solvent stream, a recycle catalyst rich stream, a raffinate stream, and an impurity rich waste stream.